1. Field of the Invention
The present invention relates to a sheet conveying apparatus and an image forming apparatus.
2. Description of the Related Art
With reference to conventional image forming apparatuses such as copying machines, printers, and facsimiles, an image forming portion has a sheet conveying apparatus which conveys a sheet which is a recording paper. For example, the sheet conveying apparatus has a skew feeding correction portion which performs skew feeding correction of the sheet in order to adjust the posture and position of the sheet until the sheet is conveyed to the image forming portion.
As such a skew feeding correction portion, an active skew feeding correction system which corrects skew feeding while the sheet is conveyed without once stopping the sheet in order to increase throughput such as image formation by making an interval between sheets (between papers) smaller has been suggested (referred to Patent documents 1 and 2).
FIG. 15 is a diagram illustrating a structure of a conventional skew feeding correction portion which performs skew feeding correction of the sheet by such an active skew feeding correction system. In FIG. 15, two skew feeding detection sensors 201a and 201b are provided at a sheet conveying path. The skew feeding detection sensors 201a and 201b are disposed at a predetermined interval in a direction perpendicular to the sheet conveying direction (hereinafter referred to as a width direction).
Skew feeding correction rollers 222a and 222b are disposed at a predetermined interval on the same axis in the width direction and they are driven by independent drive sources 221a and 221b. Further, pressure rollers 223a and 223b energized by a force means (not illustrated) are pressure-weld to the skew feeding correction rollers 222a and 222b. 
Here, in the skew feeding correction portion having such a structure, when the edge of the sheet P conveyed from the upstream crosses each of the skew feeding detection sensors 201a and 201b, a signal indicating that the sheet P crossed is output from the skew feeding detection sensors 201a and 201b. Then, the inclination of the edge of the sheet is detected based on the signal and the sheet conveying speed of the skew feeding correction rollers 222a and 222b is controlled to correct skew feeding of the sheet P.
Thus, in the active skew feeding correction system, skew feeding correction is performed without stopping the conveyance of the sheet, which allows the sheet conveying efficiency to be improved. It can be contemplated to improve the image formation speed substantially without increasing a process speed of image formation in the image forming apparatus. Therefore, the use of the active skew feeding correction system can respond to an increase in speed of image formation in the image forming apparatus in recent years.
In the sheet conveying apparatus having such a conventional skew feeding correction portion, the sheet is rotated by the skew feeding correction rollers when skew feeding is corrected. Thus, when the sheet is nipped by a driving roller located at the upstream of the skew feeding correction roller, the sheet may be drawn out from the driving roller or the sheet, and may be twisted, which causes damage to the sheet.
On the other hand, when the sheet is not nipped by the driving roller located at the upstream of the skew feeding correction roller at the time of skew feeding correction, the speed difference between the skew feeding correction rollers becomes larger as skew feeding of the sheet becomes larger. Thus, when the speed difference between the skew feeding correction rollers becomes larger, the sheet is slipped over the skew feeding correction roller. As a result, an accuracy of skew feeding correction is deteriorated or damage on the sheet is caused.